Presence detectors may be implemented using a variety of technologies. For example, pneumatic tubes or hoses may be placed across a roadway to detect the pressure of a vehicle as its tires roll over the tubes or hoses. Such detectors operate through physical contact with the object being detected. In another example, an optical light beam emitter and sensor system may detect the presence of an object when the object interrupts a projected light beam. In addition, in-ground inductance loops may detect a vehicle in close proximity by detecting a change in magnetic inductance. Other examples of presence detectors include video detectors and audio detectors.
Time-of-flight (ToF) presence detectors are used in various applications to detect the presence of objects within a specified field of detection. ToF presence detectors generally include one or more optical devices, such as optical emitters and optical sensors, for example. Unlike pneumatic tubes, optical devices in ToF presence detectors do not require physical contact with the item being detected. Unlike inductance loops, optical devices in ToF presence detectors can sense an object regardless of the magnetic properties of the object. Further, unlike a simple optical beam interruption system, ToF detectors can determine the distance between the detector and the object.
ToF presence detectors may be used to detect the presence of an animate object (e.g. a human). Detection of an animate object can be used to detect malicious intrusions in a premises or a protected area, or to ensure that no person is present in a dangerous area before executing a maneuver. Detection of an animate object is also useful in the field of human-machine interaction, where it is desirable to detect the presence of humans in the vicinity of a machine. As an example, ToF presence detectors may be used to detect whether a human is approaching a device (e.g. a computer), and such detection can cause the device to unlock or exit a low-power state in advance of the human making physical contact with the device or a peripheral component (e.g. a mouse or a keyboard) in communication with the device. As a further example, ToF presence detectors may be used to detect whether a human has exited a sensor detection area, and such detection can cause the device to turn off, enter a low-power state, or enter a locked mode (e.g. for security reasons).
Current ToF presence detectors may suffer from false positives, where the detector is unable to distinguish a dormant animate object (e.g. a stationary or immobile human) from an inanimate object (e.g. a chair). Consequently, there may be a need for improved ToF presence detectors that minimize or substantially eliminate such false positives.